1. Field of the Invention
The invention relates to improvements in a shaft sealing means and, more particularly, to a shaft sealing means for use with high pressure fluid, to directly seal such high pressure fluid acting between a rotary shaft and a body.
2. Description of the Prior Art
In a hydraulic pump/motor having a rotary shaft and an oil seal for sealing the rotary shaft, it is important to prevent fluid under pressure from escaping over the oil seal. This has been accomplished by providing drain means through which the pressurized fluid can be drawn to the outside so that the oil seal is not exposed to direct high pressures.
Where this arrangement is difficult to implement for practical reasons, another arrangement has been employed as shown in FIG. 1 wherein between the rotary shaft 1 and the body 2 there are provided a U-packing or oil seal 7, a spacer 4 retaining the oil seal 7 in position, a snap ring 3 for retaining the spacer, and a shim 8 which provides a proper clearance between the oil seal 7 and the spacer 4. While this arrangement is satisfactory for use with a relatively low pressure fluid, it has been found that its usefulness is limited in applications where a high pressure fluid is employed. That is, the oil seal 7 has its lip 9 in sealing cooperation with the rotary shaft 1 to provide an adequate seal between the rotary shaft 1 and the body 2 with a low fluid pressure on the order of 5 kg/cm.sup.2. As the pressure at the high pressure side of the seal is increased, however, the oil seal 7 is pressed toward the spacer 4 causing it to protrude into the gaps between the spacer 4 and the rotary shaft 1 and between the spacer 4 and the body 2. With the fluid pressure further increased, the oil seal 7 having its lip 9 in close contact with the rotary shaft 1 slightly rotates with rotation of the rotary shaft 1 to generate strong frictional forces between the oil seal 7 and the spacer 4. This produces oil seal contact surface stripping, a deformed or damaged oil seal and oil seal seizure under generated heat thereby causing leakage of the pressurized fluid.